Image Registration Procedures
For image registration several different procedures can be used. The most common process is the automatic image registration on the base of bone structure. Soft tissue fusion can be made with kV CT or CBCT imaging. This is of great significance because the majority of tumours are soft tissue. Of course, manual image registration can be performed with each system, but this is time consuming and highly subjective. Image registration with EPID is available only with reference markers (mostly 3 gold markers), which must be placed onto rigid anatomical sites using a surgical procedure. They are clearly identified by EPID and portal image can compare with DRR. The displacement vector can be determined by using markers. This is necessary for set-up correction. The verification images are usually made in two directions (anterior-posterior and lateral).
The same slice for treatment planning CT and MV-CBCT of a lung tumour. The tumour can be identified on the both image sets, which allows the IGRT on the base of soft tissue fusion.
Treatment planning CT image with isocentre (left side) and verification MV-CBCT image with isocentre of the treatment machine (right side) for pelvic irradiation.
Treatment planning CT image and verification kV-CBCT image fusion for pelvic irradiation.
Set –up verification with EPID for prostate irradiation. The upper left image is the DRR image, next to is the verification image made by the EPID. The image fusion was made on the base of bone structure. The lower left image is the fusion of images and next to it the set-up error in all tree direction (0.4, 0.2 és0 cm).
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